Method of coring holes in castings



Aug. 4, 1959 J. CHINI 2,897,556

METHOD OF CORING HOLES IN CASTINGS Filed Sept. 4, 1957 INVENTOR (/0 SEP/-/ C/mv/ 2,897,556 Merl-ion F CoRiNG HOLES 1N CASTINGS Joseph Chini, West Hempstead, N.Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application September 4, 1957, Serial No. 681,943

3 Claims. (Cl. 22-200) This invention relates to improvements in the art of founding or metal casting, and more particularly to the coring of relatively long slender holes in sand castings.

The usual practice in producing a sand casting having a hollow portion such as a hole is to employ a core made of sand mixed with some form of binder and baked or otherwise treated to make it self supporting. The core is suspended in the desired position in the mold to form the hole. After casting, the core is broken up and removed.

When long slender holes are required, having a length to diameter ratio of for example ten or more, the sand core becomes impractical because it is likely to be deformed or broken by the impact of the molten metal during pouring. Such holes have been produced by the use of tubular cores made of a metal having a substantially higher melting point than the metal to be cast, the core being left in the casting. This method has certain disadvantages that result from the necessary dissimilarity between the core metal and the cast metal. The core does not actually become a part of the casting, but is merely embedded in it. Voids or blows tend to form around the core.

If the finished casting is to be used in an application involving heat transfer between the body of the casting and a fiuid passing through the holes, the cast-in tubular core reduces its efiiciency. If the wall of the core is made thin to minimize its effect on the performance of the device, the core may buckle or bend while the casting is being poured.

According to the present invention, the core is formed of a rod of heat-resistant material slightly smaller in cross section than the hole to be cast, closely surrounded by a braided tubular sheath of refractory or high temperature resistant material. After the casting has cooled, the rod is removed, leaving the interior of the tubular sheath unsupported. The sheath can then be removed simply by pulling one of its ends, since the tension causes the braid to collapse to a diameter substantially less than that of the hole.

In the drawing, Fig. 1 shows a hole core of the type used in the practice of this invention.

Fig. 2 is a sectional view of a complete sand mold inv corporating the hole core of Fig. 1,

Fig. 3 is a cross sectional View of a portion of the structure of Fig. 2, taken in the plane 33, and

Fig. 4 is a sectional view of a casting made in the mold shown in Fig. 2, after removal of the core rod but before removal of the braided sheath.

The core shown in Fig. 1 includes a rod 1, somewhat longer than the hole to be cored, surrounded by a braided sheath 2 which, when stretched to a close fit on the rod 1, is also somewhat longer than the hole to be cored but preferably shorter than the rod. The diameter of the rod is such that when the sheath 2 is placed on the rod as shown, the outer surface of the sheath conforms substantially to the inner surface of the desired hole.

The rod 1 may be made of any material capable of retaining its shape under the temperature and mechanical stresses arising during the casting operation. In casting aluminum, for example, stainless steel drill rod has been found satisfactory. The sheath 2 is made of material that will not be affected by the temperature of the melt; glass fiber is satisfactory for aluminum.

It is important that neither the inner core 1 nor the sheath 2 liberates any substantial amount of gas at the molding temperature. In this connection it should be noted that glass fiber braided tubing as obtained commercially may be treated with an enamel which decomposes at high temperatures. Such tubing should be fired at a temperature high enough to remove any gasforming substance before it is used in coring.

The core is placed in the mold 3 and supported in any suitable manner, for example by the mold itself as shown in Fig. 2. In this example, the core lies in the plane of partition between the upper and lower parts 4 and 5 of the mold. Both ends of the core extend into the sand beyond the mold cavity so that they will be exposed when the casting is removed from the mold. Before assemblying the mold, the ends of the sheath are pulled out toward the ends of the rod, causing the braided tubing to contract and fit closely around the rod. The ends of the sheath should also extend beyond the mold cavity as shown.

Fig. 3 shows how the cast metal surrounds the sheath 2, which is held in place by the rod 1. The braided sheath is sufficiently porous to permit the escape of gas and heated air, but is not open enough to permit the cast metal to flow into contact with the rod 1.

After the casting has cooled, it is removed from the mold. The rod 1 is removed from the sheath. In the case of straight holes cast in aluminum, the rod will usually fall out of its own weight when placed in a vertical position. The braided sleeve is removed by pulling one of its ends. The tension reduces the cross section of the braid, disengaging it from any minor projections of cast metal into the weave and permitting it to be withdrawn through one end of the hole.

The interior surfaces of holes cast as described are clean and free of blow holes or similar imperfections. A faint impression of the characteristic pattern of the braid weave may remain; however, this is ordinarily so slight as to be of no practical importance.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

l. The method of coring a hole in a casting, comprising the steps of inserting a rod in a braided sleeve of heat resistant material, said rod being of a material which retains its shape at the temperature of the molten material to be cast, stretching said sleeve longitudinally to make it conform closely to the surface of said rod, securing the sleeve-covered rod in the desired position in the mold, pouring the casting, removing the rod from the sleeve after solidification of the casting, and applying tension to the sleeve to reduce its cross sectional dimensions and facilitate its removal from the cast hole.

2. In casting aluminum, the method of coring a hole comprising the steps of inserting a steel rod in a braided sleeve of glass fiber material, stretching said sleeve longitudinally to make it conform closely to the surface of said rod, securing the sleeve-covered rod in the desired position in the mold, pouring the casting, removing the rod from the sleeve after solidification of the casting,

and applying tension to the sleeve to reduce its cross sectional dimensions and facilitate its removal from the cast hole.

3. The method of coring a hole in a casting, comprising the steps of enclosing an inner core element of slightly smaller cross section than the hole to be. cored with a closely fitting braided sleeve of heat resistant material, securing the sleeve-covered element in the desired position in the mold, removing the inner core element from the sleeve after solidification of the casting, and applying tension to the sleeve to reduce its cross sectional dimensions and facilitate its removal from the cast hole.

References Cited in the file of this patent UNITED STATES PATENTS Dalton Nov. 12, 1957 

